Polymer composites have been used in a variety of fields, such as dental restoration and orthopedic implants. Natural biological structures, such as tooth, bone, and shell are composites of nanoscale or submicroscale hard inorganic building blocks (minerals) and soft organic matters (proteins). Metals, however, are the dominant implant materials in medical markets due to the availability of metals and their mechanical properties. Orthopedic metal implants, however, create significant concerns. Metal implants often need to be removed, and even those that are not removed may cause adverse effects such as formation of excess scar tissue, infection, weakened bone, and immune sensitivity. Synthetic ceramics, polymers, and their composites may provide better biological properties but their applications have been hampered by inadequate mechanical properties. For example, the compressive and/or tensile strength of hydroxyapatite-collagen (HA/Col) composites are typically much lower than cortical bone and metals.
In dental applications, amalgam provides a median survival lifespan of 13 years. Resin-based composites typically have a median survival lifetime of 5-7 years because of inadequate mechanical properties and poor bonding to tooth material. Still, polymers are preferred due to aesthetic and safety concerns with amalgam.
To improve the properties of synthetic polymer composites, fillers have been added to these materials. For example, some polymer composites have been reinforced with nanowhiskers. Some dental composites have used silica or silicate nanoparticles as fillers, and some orthopedic in-situ and ex-situ composites have been reinforced with hydroxyapatite, either in the form of short nanofibers and nanowhiskers. However, the mechanical properties of the composites reinforced by nanoparticles, short nanofibers, or nanowhiskers show limited improvement in mechanical properties such as strength and toughness and may not be sufficient to meet the requirements of various applications.
Therefore, there is a need to provide a new and improved synthetic composite with enhanced mechanical properties sufficient for biomedical applications.